InternalAdd method
      
void
InternalAdd(
    
- TEntry entry
Implementation
void InternalAdd(TEntry entry) {
  entry.addOnChangeEvent(this._EntryChanged);
  this._entries[entry.Key] = entry;
  this._addedEntries.add(entry.Key);
  this._removedEntries.remove(entry.Key);
  this.Changed();
}